InCl3/Al mediated pinacol coupling reactions of aldehydes and?ketones in aqueous media

Article abstract of DOI:10.1016/j.tet.2006.10.061

A systematic work on the homo-pinacol coupling reactions of benzophenones, aldehydes, and acetophenones in aqueous media with InCl₃/Al is described for the first time, in which various 1,2-diols are obtained in moderate to good yields.

Full text of DOI:10.1016/j.tet.2006.10.061

Tetrahedron 63 (2007) 429–434
InCl3/Al mediated pinacol coupling reactions of aldehydes
and ketones in aqueous media
b,
Chunyan Wang,a Yuanjiang Pana, and Anxin Wu
*
*
aDepartment of Chemistry, Zhejiang University, Hangzhou 310027, PR China
bKey Laboratory of Pesticide and Chemical Biology of Ministry of Education, Central China Normal University,
Wuhan 430079, PR China
Received 18 July 2006; revised 19 October 2006; accepted 23 October 2006
Available online 9 November 2006
Abstract—A systematic work on the homo-pinacol coupling reactions of benzophenones, aldehydes, and acetophenones in aqueous media
with InCl3/Al is described for the first time, in which various 1,2-diols are obtained in moderate to good yields.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
whichstimulatesfurtherexplorationofthereactivityofInCl3.
InCl3-catalyzed pinacol couplings of aromatic carbonyl
compounds by using aluminum in the presence of chlorotri-
methylsilane have been reported. But in this reaction anhy-
drous THF as solvent under nitrogen atmosphere was
required.16a,16c Up to now, there is no report on the pinacol
coupling reactions mediated by InCl3/Al in aqueous media.
We herein present a systematic study first on the pinacol
coupling reactions of aromatic aldehydes and ketones by
using InCl3/Al in aqueous media.
From atom economy perspective, the reductive pinacol reac-
tion of two carbonyl compounds is a powerful way to form
the C–C bond of 1,2-diols.1 Since the first report of the reac-
tion of acetone with sodium in 1858,2 various low-valent
metals such as Al,3 Sm,4 V,5 Mg,6 Zn,7 Mn,8 Sn,9 Ti,10 Ce,11
Te,12 U,13 Cr,14 Ga,15 and In16 have been used to promote this
reductive coupling reaction. Among these methods, some re-
quire absolutely anhydrous system under inert atmosphere,
and some reagents and solvents are costly, moisture-sensi-
tive, and toxic. In order to find environmental friendly con-
dition, it is very attractive to develop a new convenient
method for the pinacol coupling by utilizing less toxic re-
agents and solvents. During past decades, great efforts have
been made by chemists to explore environmentally benign
systems for pinacol reaction. Different catalysts/co-catalysts
in aqueous media including TiCl3, VCl3/Al, Mn/HOAc,
Al/MF, etc. have been reported with promising results.17
2. Results and discussion
2.1. Optimization of InCl3/co-reductant mediated
pinacol coupling reaction of benzophenone
In our initial experiment, we examined the effect of the
different metallic co-reductants and solvents on the pinacol
coupling of benzophenone (Table 1). A mixture of benzo-
phenone (1 mmol), indium chloride (1 mmol), NH4Cl (1 g),
commercial aluminum powder (3.5 mmol), and 50% aque-
ous EtOH (4 mL) was stirred at 80 ꢀC for 5 h. Compound
2a was obtained as the only product in high yield (Table 1,
entry 1). The absence of NH4Cl decreased the yield greatly
(Table 1, entry 2). No desired product was obtained without
indium chloride (Table 1, entry 3). When 1 mmol of indium
chloride was combined with 3.5 mmol of co-reductant Zn or
Fe, no reaction occurred (Table 1, entries 4 and 5). But sim-
ilar treatment with co-reductant Mg afforded the pinacol 2a
in 22% yield (Table 1, entry 6). These results showed that
metallic Al was more efficient as a co-reductant than others.
Several solvents, such as EtOH, H2O, 50% aqueous EtOH
(pH¼1–2), 50% aqueous EtOH (pH¼11–12), and THF,
Water offers several advantages compared with organic sol-
vents because of its low cost, safety, and operational simpli-
city. So recently organic reactions in water or aqueous media
have attracted chemists’ great interest.18
For a few decades, more attention has been paid to the devel-
opment of new synthetic methods using indium chloride,
which is nontoxic and compatible with water and air.19 Re-
cently, we have reported some InCl3-mediated reactions,20
Keywords: InCl3/Al; Pinacol coupling; Benzophenones; Aldehydes; Aceto-
phenones.
* Corresponding authors. Tel.: +86 571 8795 1264; fax: +86 571 8795 1629
(Y.P.); e-mail addresses: cheyjpan@zju.edu.cn; chwuax@mail.ccnu.
edu.cn
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.10.061

430
C. Wang et al. / Tetrahedron 63 (2007) 429–434
Table 1. Effect of indium chloride, metallic co-reductant, and solvent on the
accordingly. The reaction at the room temperature gave the
trace benzhydrol as the only product (Table 2, entry 6).
These results proved that the higher temperature is in favor
of the pinacol coupling of benzophenone by using InCl3/
Al reagent. With the emphasis on the search for the pinacol
coupling of aldehydes and ketones to form carbon–carbon
bond, 80 ꢀC was chosen as the optimized temperature.
pinacol coupling of benzophenonea
OH OH
O
InCl3
Ph
Ph
metallic co-reductant
Ph Ph
1a
Ph Ph
2a
Entry Reductant
Solvent (mL)
NH4Cl Time Yieldc
(g)
(h)
(%)
2.2. InCl3/Al mediated pinacol coupling of substituted
benzophenones in 50% aqueous alcohol
1
2
3
4
5
6
7
8
9
InCl3/Al
InCl3/Al
Al
InCl3/Zn
InCl3/Fe
InCl3/Mg
InCl3/Al
InCl3/Al
InCl3/Al
EtOH (2), H2O (2)
EtOH (2), H2O (2)
EtOH (2), H2O (2)
EtOH (2), H2O (2)
EtOH (2), H2O (2)
EtOH (2), H2O (2)
EtOH (4)
1
—
1
1
1
1
1
1
—
5
5
92
62
0
0
0
22
0
15
67
11
11
11
11
11
11
11
Under the optimized conditions (Table 1, entry 1), various
substituted benzophenones were investigated to give a series
of 1,10,2,20-tetraaryl substituted 1,2-diols (2a–g) (Table 3).
From these results, we found that 2a–c were obtained in ex-
cellent yields without formation of by-product due to reduc-
tion of the carbonyls to the corresponding alcohols (Table 3,
entries a–c). Benzophenones bearing electron-donating
groups (1d,e) para to ketones were reduced to the corre-
sponding pinacols in the moderate yields even after 11 h
(Table 3, entries d and e). Unfortunately, the reactions of
benzophenones bearing electron-withdrawing groups (1f,g)
para to ketones with InCl3/Al reagent at 80 ꢀC for 3 h gave
miscellaneous products, in which most starting materials had
been consumed (Table 3, entries f and g). On the other hand,
lower temperature gave pinacols in moderate yields (Table 3,
entries f0 and g0) along with a small quantity of the corre-
sponding alcohols. Unexpectedly, benzophenone bearing a
chlorine group (1h) ortho to ketone only gave the corre-
sponding alcohol as the main product.
H2O (4)
EtOH (2), H2O (2),
pH¼1–2b
10
InCl3/Al
InCl3/Al
InCl3(Cat.)/Al EtOH (2), H2O (2)
EtOH (2), H2O (2),
pH¼11–12b
—
11
13
11
THF (4)
1
1
11
11
Trace
30
12d
a
Reaction conditions: benzophenone (1 mmol), indium chloride (1 mmol),
co-reductant Al, Zn, Fe or Mg (3.5 mmol), 80 ꢀC.
pH was adjusted by concentrated hydrochloric acid or solid sodium
hydroxide.
Isolated yield.
InCl3 (20 mol %) was used.
b
c
d
were also surveyed by using InCl3/Al as the reducing agent.
Most of the reactions worked poorly except that 50% aque-
ous EtOH (pH¼1–2) gave a moderate yield (Table 1, entries
7–11). When catalytic InCl3 was used, only 30% yield was
obtained (Table 1, entry 12).
Table 3. Pinacol coupling of substituted benzophenones by using InCl3/Al
reagenta
In the following experiment, different temperatures were
also surveyed by using benzophenone as an example [benzo-
phenone (1 mmol), indium chloride (1 mmol), co-reductant
Al (3.5 mmol), and 50% aqueous EtOH (4 mL)] (Table 2).
Only compound 2a was obtained at 80 or 90 ꢀC (Table 2, en-
tries 1 and 2). However, the lower temperatures (50–70 ꢀC)
yielded two products, the corresponding alcohol—benz-
hydrol (BH) and the coupling product—benzpinacol (BP)
(Table 2, entries 3–5). It was interesting that when the reac-
tion temperature dropped, the ratio of BH/BP increased
HO OH
Ar2
O
InCl3/Al, NH4Cl
EtOH-H2O, 80 °C
Ar2
Ar2
Ar1
1a-h
Ar1
Ar1
2a-g
Entry
Ar1
Ar2
Time (h)
Yield of 2c (%)
a
b
c
d
e
C6H5
4-CH3C6H4
4-FC6H4
4-(OCH3)C6H4
4-(OCH3)C6H4
4-ClC6H4
4-(C6H5)C6H4
4-ClC6H4
4-(C6H5)C6H4
2-ClC6H4
C6H5
C6H5
5
5
5
2a, 92
2b, 90
2c, 98
2d, 48
2e, 72
Mixture
Mixture
2f, 64
4-FC6H4
4-FC6H4
C6H5
C6H5
C6H5
11
11
3
f
g
f0
g0
h
3
C6H5
C6H5
C6H5
5b
Table 2. Effect of the temperature on benzhydrol (BH):benzpinacol (BP)
ratios in the reduction of benzophenone 1aa,b
5b
5
2g, 65
—, (52)d
OH OH
OH
O
InCl3/Al
+
Ph
Ph
a
Reaction conditions: 1 (1 mmol), indium chloride (1 mmol), Al powder
(3.5 mmol); 80 ꢀC except pointed out especially.
60 ꢀC.
Ph
Ph
Ph
Ph Ph
Benzpinacol
BP
Ph
Benzhydrol
BH
b
c
d
Isolated yield.
Only the corresponding alcohol was obtained.
Entry
T (ꢀC)
Time (h)
BHb
BPb
Total yield
(BH+BP)c (%)
1
2
3
4
5
6
90
80
70
60
50
rt
5
5
5
6
11
26
—
—
24
50
64
100
100
100
76
50
36
93
92
94
90
55
Trace
2.3. InCl3/Al mediated pinacol coupling of substituted
benzaldehydes in 50% aqueous alcohol
When a mixture of benzaldehyde, Al powder, InCl3, and
NH4Cl in 50% aqueous EtOH was stirred for 2 h at 80 ꢀC,
4a was obtained in 88% yield (meso/dl¼40/60). Similar
treatment of substituted benzaldehydes 3b–h gave 4b–g
as shown in Table 4. In all cases except for 3g and 3h, 4
was obtained in satisfactory yield with poor meso/dl ratios.
—
a
Reaction conditions: benzophenone 1a (1 mmol), indium chloride
(1 mmol), Al powder (3.5 mmol).
The ratios were determined by isolated yields and did not represent yields.
Total isolated yield (BH+BP).
b
c

C. Wang et al. / Tetrahedron 63 (2007) 429–434
431
Table 4. Pinacol coupling of benzaldehydes 3 by using InCl3/Al reagenta
entry g). Similarly, the reaction of 5h gave 5i. For 5i and
5j, no reaction occurred. From these results, we found that
the compounds containing nitro group and esters were
incompatible with the InCl3/Al reagent, which could be
reduced or hydrolyzed, respectively.
R
InCl3/Al, NH4Cl
EtOH-H2O, 80 °C
CH CH
OH OH
CHO
R
3a-h
R
4a-g
In order to investigate the limitation of the scope of the
substrates for this reaction condition, the pinacol coupling
of aliphatic ketone was investigated, for example, cyclohep-
tanone. After carrying out the reaction of cycloheptanone by
using InCl3/Al reagent in 50% aqueous EtOH at 80 ꢀC for
11 h, no reduced product was monitored.
Entry
R
H
2-Cl
4-Cl
2-F
2-Br
4-CH3
4-OCH3
2-OCH3
Time (h)
meso/dlb
Yield of 4c (%)
a
b
c
d
e
f
2
2
2
2
2
11
11
11
40/60
66/34
30/70
62/38
71/29
56/44
—
4a, 88
4b,78
4c, 80
4d, 84
4e, 80
4f, 78
g
h
4g, trace
—, (18)d
The mechanism of metal reduction of the carbonyl com-
pound is generally believed to proceed through the coupling
of a ketyl radical anion formed by electron transfer from the
metal to the carbonyl substrate.1 In our experiment, the sim-
ilar mechanism is possible. Activated indium generated in
situ by InCl3/Al reduces the carbonyl to the radical anion
to form the pinacol product. Although the reaction in abso-
lute water only gives unsatisfactory yield (Table 1, entry 8),
in this reaction system water seems to be critical. This gains
support from the fact that no reduced product was obtained
in the reactions of benzophenone in absolute ethanol even
after stirred for 11 h (Table 1, entry 7). It is possible that
the coupling of ketyl radical anions seems to take place in
an aqueous medium at a much faster rate compared to further
electron transfer from the metal surface resulting in prefer-
ential formation of the diol over the reduced alcohol.21
Moreover, it was proved that high temperature is in favor
of the coupling of ketyl radical anions. According to all the
experimental results, it was thought that carbonyl com-
pounds bearing electron-withdrawing group have higher
reactivity than those of bearing electron-donating groups
in the pinacol coupling generally. Steric hindrance ortho to
carbonyl group could affect the coupling of ketyl radical an-
ions in which the effect is the most in pinacol couplings of
benzophenones and the least in those of benzaldehydes. As
compared with commercial metal indium, indium generated
in situ can avoid the refractory metal oxide surface problem
in aqueous media.
—
a
Reaction conditions: 3 (1 mmol), indium chloride (1 mmol), Al powder
(3.5 mmol), NH4Cl (1 g), 80 ꢀC.
Determined by 1H NMR.
Isolated yield.
Only the corresponding alcohol was obtained.
b
c
d
Benzaldehydes bearing electron-donating groups (3g,h)
were reduced slowly compared with 3a–e. The coupling re-
action of 3g at 80 ꢀC for 11 h in 50% aqueous EtOH only
gave a trace yield. However, the corresponding alcohol as the
main product was obtained in the reduction of 3h (Table 4,
entry h). It was supposed that steric hindrance plays a great
role in the pinacol coupling. Large group ortho to aldehyde
cumbers coupling of the intermediate.
2.4. InCl3/Al mediated pinacol coupling of substituted
acetophenones in 50% aqueous alcohol
The InCl3/Al reagent was also effective for the coupling of
substituted acetophenones 5a–e (Table 5, entries a–e). As
compared with 1 and 3, pinacol reaction of 5 was slightly
sluggish. When the coupling reactions of 5a–e with InCl3/Al
reagent were carried out at 80 ꢀC for 11 h, 6a–e were ob-
tained in less than 64% yield. Acetophenone 5f bearing para
nitro-group was reduced to 5g. Considering possible insuffi-
ciency of the reducing agent, the coupling of 5g was inves-
tigated and most starting material was obtained (Table 5,
3. Conclusion
Table 5. Pinacol coupling of acetophenones 5 by using InCl3/Al reagenta
R
O
CH3CH3
We have demonstrated that InCl3/Al reagent can be used for
the pinacol reactions of benzophenones, benzaldehydes, and
acetophenones in aqueous media successfully. The effect of
the different groups on the yield and the stereoselectivity has
been also investigated systematically by using the optimized
reaction condition. The important advantage of the present
method includes (a) operational simplicity, (b) less toxic re-
agents and solvent. Therefore, it is considered to be an envi-
ronmental friendly synthetic method. Further investigation
of the mechanism of this reaction is currently underway.
R
InCl3/Al, NH4Cl
EtOH-H2O, 80 °C
CH3
OH OH
6a-e
R
5a-j
Entry
R
H
meso/dlb
Yield of 6c (%)
a
b
c
d
e
f
g
h
i
49/51
46/54
52/48
45/55
45/55
—
—
—
—
—
6a, 52
6b, 33
6c, 31
6d, 64
6e, 48
5g, 98
—
5i, 98
—
—
4-CH3
2-CH3
4-Cl
2-Br
4-NO2
4-NH2
4-CH3COO
4-OH
4. Experimental
4.1. General
j
3-OCH3
a
Reaction conditions: 5 (1 mmol), indium chloride (1 mmol), Al powder
(3.5 mmol), NH4Cl (1 g), 80 ꢀC, 11 h.
Determined by 1H NMR.
1
The H NMR and 13C NMR spectra were obtained with
b
c
Isolated yield.
a Bruker AVANCE DRX-500 NMR spectrometer (1H,

432
C. Wang et al. / Tetrahedron 63 (2007) 429–434
500 MHz; 13C, 125 MHz) with TMS as internal standard and
CDCl3 as solvent. The ESI-MS spectra were taken on a
Bruker Esquire 3000 plus spectrometer. Precoated thin-layer
plates of silica gel 60 GF254 (Qingdao Haiyang Chemical
Co. Ltd, Qingdao, China) were used for analytical purposes.
All the benzophenones, benzaldehydes, and acetophenones
were purchased from J&K chemical Co., or other commer-
cial suppliers and were used after appropriate purification
(distillation).
4.2.6. 1,2-Diphenyl-1,2-di(4-chlorophenyl)-ethane-1,2-
1
diol (2f). White solid; H NMR (CDCl3, 500 MHz) d 2.96
(s, 2H, OH), 7.08–7.41 (m, 18H, Ph); 13C NMR (CDCl3,
125 MHz) d 82.90, 127.51, 127.55, 127.65, 127.70, 127.76,
128.41, 128.48, 130.24, 130.27, 132.98, 133.16, 142.86,
143.36, 143.66; ESI-MS m/z: 456.7 [M+Na]+.
4.2.7. 1,2-Diphenyl-1,2-di(4-phenylphenyl)-ethane-1,2-
1
diol (2g). White solid; H NMR (CDCl3, 500 MHz) d 3.09
(s, 2H, OH), 7.19–7.57 (m, 28H, Ph); 13C NMR (CDCl3,
125 MHz) d 83.22, 126.07, 127.11, 127.21, 127.44, 127.52,
128.71, 128.78, 128.87, 129.21, 129.28, 139.65, 140.59,
143.40, 143.40, 144.24; ESI-MS m/z: 540.8 [M+Na]+.
4.2. General procedure for the pinacol coupling reac-
tions of substituted benzophenones in 50% aqueous
alcohol
A suspension of benzophenones 1 (1 mmol), indium chlo-
ride (1 mmol), Al powder (3.5 mmol), and NH4Cl (1 g) in
50% aqueous EtOH was stirred vigorously at 80 ꢀC until
the reaction was completed (monitored by TLC). The reac-
tion was quenched with 1 N HCl (3 mL) and extracted with
ether (3ꢁ20 mL). The combined organic layers were washed
with brine, dried over sodium sulfate, and filtered. The
filtrate was concentrated under reduced pressure. Purifica-
tion by silica gel column chromatography (200–300
mesh) with petroleum ether (60–90 ꢀC) and ethyl acetate
as eluent afforded the corresponding products (2a–g, the
product of 1h).
4.2.8. The product of 1h: (2-chlorophenyl)-phenyl-meth-
1
anol. White solid; H NMR (CDCl3, 500 MHz) d 2.45 (s,
1H, OH), 6.18 (s, 1H, CH), 7.20–7.59 (m, 9H, Ph); 13C NMR
(CDCl3, 125 MHz) d 83.13, 127.10, 127.44, 128.72, 144.25;
ESI-MS m/z: 240.7 [M+Na]+.
4.3. General procedure for the pinacol coupling
reactions of substituted benzaldehydes in 50%
aqueous alcohol
General procedure for the pinacol coupling reactions of
substituted benzaldehydes is similar to that of benzophe-
nones. The corresponding products (4a–f, the product of
3h) were obtained.
4.2.1. 1,1,2,2-Tetraphenyl-ethane-1,2-diol (2a). White
1
solid; H NMR (CDCl3, 500 MHz) d 3.03 (s, 2H, OH),
7.15–7.20 (m, 12H, Ph), 7.28–7.30 (m, 8H, Ph); 13C NMR
(CDCl3, 125 MHz) d 83.13, 127.10, 127.44, 128.72, 144.25;
ESI-MS m/z: 389.0 [M+Na]+.
4.3.1. 1,2-Diphenyl-ethane-1,2-diol (meso/dl mixture)
(4a). White solid; H NMR (CDCl3, 500 MHz) d 2.85 (br,
1
2H, OH), 4.67 (dl, s, 2H, CH), 4.80 (meso, s, 2H, CH), 7.09–
7.31 (m, 10H, Ph); 13C NMR (CDCl3, 125 MHz) d 78.12,
79.21, 127.08, 127.22, 128.03, 128.19, 128.24, 128.32,
139.87, 139.98; ESI-MS m/z: 236.6 [M+Na]+.
4.2.2. 1,2-Diphenyl-1,2-di-p-tolyl-ethane-1,2-diol (2b).
White solid; H NMR (CDCl3, 500 MHz) d 2.25 (dl, s,
1
6H, Me), 2.26 (meso, s, 6H, Me), 2.99 (s, 2H, OH), 6.94–
6.97 (m, 4H, Ph), 7.11–7.15 (m, 10H, Ph), 7.29–7.33
(m, 4H, Ph); 13C NMR (CDCl3, 125 MHz) d 21.18, 83.10,
126.91, 126.98, 127.39, 127.41, 128.21, 128.24, 128.66,
128.71, 128.76, 128.81, 136.65, 136.74, 141.37, 141.42,
144.61, 144.64; ESI-MS m/z: 416.9 [M+Na]+.
4.3.2. 1,2-Di(2-chlorophenyl)-ethane-1,2-diol (meso/dl
mixture) (4b). White solid; H NMR (CDCl3, 500 MHz)
1
d 2.97 (s, 2H, OH), 5.31 (dl, s, 2H, CH), 5.56 (meso, s, 2H,
CH), 7.11–7.61 (m, 8H, Ph); 13C NMR (CDCl3, 125 MHz)
d 72.17, 73.14, 76.93, 77.18, 77.44, 126.55, 126.95, 128.91,
128.97, 129.27, 129.56, 132.74, 133.48, 136.50, 137.37;
ESI-MS m/z: 304.6 [M+Na]+.
4.2.3. 1,1,2,2-Tetrakis-(4-fluorophenyl)-ethane-1,2-diol
1
(2c). White solid; H NMR (CDCl3, 500 MHz) d 6.85–
6.89 (m, 8H, Ph), 7.23–7.25 (m, 8H, Ph); 13C NMR (CDCl3,
125 MHz) d 82.72, 114.37, 114.54, 130.39, 130.46, 139.80,
160.97, 162.93; ESI-MS m/z: 460.9 [M+Na]+.
4.3.3. 1,2-Di(4-chlorophenyl)-ethane-1,2-diol (meso/dl
mixture) (4c). White solid; H NMR (CDCl3, 500 MHz)
1
d 2.94 (br, 2H, OH), 4.60 (dl, s, 2H, CH), 5.81 (meso, s, 2H,
CH), 7.00–7.26 (m, 8H, Ph); 13C NMR (CDCl3, 125 MHz)
d 76.89, 78.65, 128.45, 128.48, 128.52, 133.99, 138.05;
ESI-MS m/z: 280.8 [MꢂH]ꢂ.
4.2.4. 1,2-Di(4-fluorophenyl)-1,2-di(4-methoxyphenyl)-
ethane-1,2-diol (2d). White solid; 1H NMR (CDCl3,
500 MHz) d 2.96 (s, 2H, OH), 3.71 (dl, s, 6H, OMe), 3.72
(meso, s, 6H, OMe), 6.67–7.41 (m, 16H, Ph); 13C NMR
(CDCl3, 125 MHz) d 55.18, 55.22, 82.72, 112.80, 113.95,
113.97, 114.11, 114.14, 129.78, 129.82, 130.43, 130.50,
130.57, 135.90, 136.16, 140.47, 158.50, 158.67, 160.57,
160.71, 162.52, 162.66; ESI-MS m/z: 484.9 [M+Na]+.
4.3.4. 1,2-Di(2-fluorophenyl)-ethane-1,2-diol (meso/dl
mixture) (4d). Viscous liquid; 1H NMR (CDCl3, 500 MHz)
d 3.09 (s, 2H, OH), 5.13 (dl, s, 2H, CH), 5.35 (meso, s, 2H,
CH), 6.88–7.43 (m, 8H, Ph); 13C NMR (CDCl3, 125 MHz)
d 70.72, 72.12, 114.93, 115.11, 115.31, 115.48, 124.04,
124.07, 124.32, 126.53, 126.63, 128.47, 128.50, 128.65,
129.49, 129.56, 129.74, 129.81, 159.32, 161.27; ESI-MS
m/z: 272.6 [M+Na]+.
4.2.5. 1,2-Diphenyl-1,2-di(4-methoxyphenyl)-ethane-1,2-
diol (2e). White solid; H NMR (CDCl3, 500 MHz) d 2.96
1
(s, 2H, OH), 3.74 (s, 6H, OMe), 6.68–7.30 (m, 18H, Ph);
13C NMR (CDCl3, 125 MHz) d 55.24, 82.97, 112.67,
126.96, 127.38, 128.72, 129.96, 136.45, 144.61, 158.39;
ESI-MS m/z: 449.0 [M+Na]+.
4.3.5. 1,2-Di(2-bromophenyl)-ethane-1,2-diol (meso/dl
mixture) (4e). Viscous liquid; 1H NMR (CDCl3, 500 MHz)
d 2.79 (s, 2H, OH), 5.30 (dl, s, 2H, CH), 5.54 (meso, s, 2H,

C. Wang et al. / Tetrahedron 63 (2007) 429–434
433
CH), 7.07–7.68 (m, 8H, Ph); 13C NMR (CDCl3, 125 MHz)
d 74.49, 75.34, 123.08, 124.13, 127.19, 127.61, 129.36,
129.38, 129.69, 129.86, 132.26, 132.92, 138.00, 138.88;
ESI-MS m/z: 392.6 [M+Na]+.
(m, 8H, Ph); 13C NMR (CDCl3, 125 MHz) d 25.06, 25.23,
78.74, 79.00, 127.03, 127.08, 127.18, 127.28, 127.41,
127.52, 143.57, 143.93; ESI-MS m/z: 420.7 [M+Na]+.
4.4.6. 1-(4-Amino-phenyl)-ethanone (5g). White solid; 1H
NMR (CDCl3, 500 MHz) d 2.49 (s, 3H, Me), 4.35 (s, 2H,
NH2), 6.62–6.64 (m, 2H, Ph), 7.78–7.80 (m, 2H, Ph); 13C
NMR (CDCl3, 125 MHz) d 26.23, 113.81, 127.63, 130.96,
151.68, 196.84; ESI-MS m/z: 135.7 [M+H]+.
4.3.6. 1,2-Di(4-methylphenyl)-ethane-1,2-diol (meso/dl
mixture) (4f). White solid; H NMR (CDCl3, 500 MHz)
1
d 2.28 (dl, s, 6H, Me), 2.32 (meso, s, 6H, Me), 2.67 (br,
2H, OH), 4.60 (dl, s, 2H, CH), 4.70 (meso, s, 2H, CH),
6.97–7.14 (m, 8H, Ph); 13C NMR (CDCl3, 125 MHz)
d 21.28, 21.31, 78.13, 78.90, 127.01, 127.19, 128.92, 129.08,
137.12, 137.16, 137.55, 137.86; ESI-MS m/z: 264.6
[M+Na]+.
4.4.7. 1-(4-Hydroxy-phenyl)-ethanone (5i). White solid;
1H NMR (CDCl3, 500 MHz) d 2.61 (s, 3H, Me), 7.12–7.57
(m, 5H); 13C NMR (CDCl3, 125 MHz) d 26.54, 115.89,
129.49, 131.59, 162.04, 199.46; ESI-MS m/z: 136.7 [M+H]+.
4.3.7. The product of 3h: (2-methoxyphenyl)methanol.
White solid; H NMR (CDCl3, 500 MHz) d 2.32 (s, 1H,
OH), 3.86 (s, 3H, Me), 4.68 (s, 2H, CH), 6.89–7.28 (m,
4H, Ph); 13C NMR (CDCl3, 125 MHz) d 55.38, 62.26,
110.33, 120.78, 128.88, 129.09, 129.18, 157.58; ESI-MS
m/z: 160.7 [M+Na]+.
1
Acknowledgements
The generous financial support of Natural Science Founda-
tion of China (20375036) is gratefully acknowledged.
4.4. General procedure for the pinacol coupling
reactions of substituted acetophenones in 50%
aqueous alcohol
Supplementary data
Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2006.10.061.
General procedure for the pinacol coupling reactions of
substituted acetophenones is similar to that of benzophe-
nones. The corresponding products (6a–e, 5g, and 5i) were
obtained.
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1
d 1.45 (dl, s, 6H, Me), 1.53 (meso, s, 6H, Me), 2.33 (s, 6H,
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1
d 1.71 (dl, s, 6H, Me), 1.72 (meso, s, 6H, Me), 2.07 (s, 6H,
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1
d 1.43 (dl, s, 6H, Me), 1.52 (meso, s, 6H, Me), 7.04–7.08
(m, 8H, Ph); 13C NMR (CDCl3, 125 MHz) d 24.94, 25.25,
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1
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